Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to a method and apparatus of maintaining image quality while reducing system fabrication cost.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for rejecting scatter x-rays from the patient, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
Typically, the detector array is fabricated from a large number of detector modules that are each separately fabricated, tested, and installed into the detector array during assembly. For instance, in one design the detector array is fabricated from 57 modules, each having 16 channels along a channel direction of the detector array. The modules of known designs may include 8, 16, 32, 64, or more pixels in a slice direction of the detector array.
However, because of the complexity of the design of the modules: to include high density interconnects, array bonding of a backlit diode, underfill, and myriad other issues, the modules are very expensive to fabricate and test. And, as complexity increases, the possibility for yield losses during module fabrication and testing increases as well. Further, the modules that make up the detector array are aligned and positioned with a high degree of accuracy with respect to one another, typically on the order of microns are required. As such, the detector array is typically fabricated in a test bay as a stand-alone unit and then the unit is installed and tested in a larger assembly bay.
In addition, in some system designs or applications it may be desirable to reduce an amount of detector coverage along the slice direction (to, for instance 8 slices of coverage) in order to reduce system cost, enabling a cost tradeoff to be made between coverage and cost. However, in other system designs or applications it may be desirable to increase an amount of coverage along the slice direction (to, for instance 16, 64, or 256 slices as examples). As such, there are multiple configurations of designs that may be desired based on z-coverage and cost tradeoffs. Each detector design, though, includes different amounts of z coverage. That is, an 8-slice detector is typically designed from 8-slice detector components, a 16-slice detector is typically designed from 16-slice detector components, etc. . . . , resulting in a different system design for each amount of coverage that is desired. As such, there is typically not a lot commonality in designs of different slice coverage, resulting in separate components and assembly and test procedures for each unique design.
Thus, there are therefore not only myriad issues associated with fabrication and testing of individual detector modules, but overall system cost, complexity, and yield are also affected because of the different detector designs having differing amounts of z-coverage. And, in some markets, such as in the developing world, there is less need for a “high-end” imaging capability as such systems may be priced out of the market while providing functionality that is of less demand (such as 64 slice or 256 slice coverage). For instance, systems having 64-slice capability or greater are directed increasingly toward the desire to image a full organ in a single rotation. However, in many markets it is more desirable to have a much more basic scanning capability, with system cost a much more important driver than high-end scanning capability. In other words, in some markets it is desirable to have an option to purchase a system that is skewed toward low cost, with users willing to forego a more high-end scanning capability.
As such, there is a need to reduce cost and complexity of detector arrays in imaging application, particularly in system designs having a more limited amount of z-coverage that are directed toward a value end of the market. Therefore, it would be desirable to design an apparatus and method to reduce cost of a CT system, while providing a basic amount of detector coverage, system and performance capability.